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var each = _.each = _.forEach = function(obj, iterator, context) {
if (obj == null) return obj;
if (nativeForEach && obj.forEach === nativeForEach) {
obj.forEach(iterator, context);
} else if (obj.length === +obj.length) {
for (var i = 0, length = obj.length; i < length; i++) {
if (iterator.call(context, obj[i], i, obj) === breaker) return;
}
} else {
var keys = _.keys(obj);
for (var i = 0, length = keys.length; i < length; i++) {
if (iterator.call(context, obj[keys[i]], keys[i], obj) === breaker) return;
}
}
return obj;
};
在underscore.js中实现_.each方法时,循环变量设置如下。for循环中的循环变量声明样式
for (var i = 0, length = obj.length; i < length; i++)
为什么显式声明了长度变量?,是不是下面的代码更简洁?
for (var i = 0; i < obj.length; i++)
它更简洁但效率更低。在第二个循环中,每次迭代都会提取'obj.length'。首先,你只是检查一个设定值。 – ChicagoRedSox